The subject matter of the present invention is a chair, in particular an office swivel chair, having a height-adjustable seat surface and an inclination-adjustable back part, a synchronous change in the position of the seat surface taking place with the adjustment of the back part. The chair has a pivot axis which runs over the width of the seat surface and is formed by joint connections on the seat support. The entire chair mechanism is arranged below the seat plate. The height and inclination are adjusted by means of springs, preferably pneumatic springs. In order to optimize the kinematics of the inclination and to set a prestress which overrides the pneumatic spring, it is customary to provide an additional helical compression spring. The pneumatic springs are actuated by adjusting levers which are arranged below the seat plate and to which the user in the seat has convenient access. If the locking of the inclination adjustment is released, the user can get from the vertical position into the inclination position by shifting his weight, the seat plate following the adjustment. Chairs of this type offer the user increased comfort, since the back part and the seat surface are advantageously matched ergonomically to the seat position assumed in each case.
The invention is furthermore concerned with a cover for the back part and also with a height-adjustable armrest.
CH-A-568 738 discloses the principle of subdividing the seat surface into a fixed thigh support and a pivotable posterior support which merges into the backrest. The subdivision is realized using hinge elements which are arranged in the side parts of the supporting frame.
CH-A-582 498 likewise proposes a chair having a pivotable backrest and a posterior support connected to it, the cover of the seat surface extending beyond the pivot axis as far as the rear part of the frame. A pneumatic spring is used for adjusting the inclination. However, it does not have a height-setting capability or an integrated adjusting mechanism.
WO-A-98/16140 discloses a chair having a pivotable back part whose rotational axis defines a rear region on the seat surface having a posterior support. One section of the back part extends as far as the rotational axis where the back part is coupled to the seat support in a hinge connection. A one-piece cushion cover is fastened to the seat support and runs from the seat surface over and beyond the rotational axis as far as the frame part behind the posterior support. The back part is composed of the back support which is coupled in the hinge connection, and of a bow-shaped back tensioner which is to be fixed over it and is inserted into the back part of the cushion cover. The cushion cover stretches as one piece over the seat surface and the back part. The back support has a transverse strut to which the cushion cover is fastened and from where it passes onto the back part. When the backrest is inclined, the seat surface is virtually stationary and only the posterior support as a cushion section follows a changed inclination, so that a complete synchronous sequence between the back part and seat surface is not realized. In addition, this chair does not have armrests.
The invention is therefore based on the object of realizing, for a chair having a pivot axis running over the seat surface, the full synchronous sequence between the pivoting movement of the back part and the seat surface. The chair mechanism is to be as uncomplicated as possible in its basic structure, and to be functionally reliable, not to need much servicing and to be convenient to operate. Furthermore, the mechanism is to be integrated inconspicuously in the chair as a compact construction. The back cover is to provide good support for the lumbar region of the user. In addition, the chair has to be fitted with height-adjustable armrests which can be adjusted conveniently and nevertheless have great stability in the setting selected. Finally, the chair is to be able to be produced in series efficiently and cost-effectively and at the same time make an original aesthetic appearance possible.
The adjusting mechanism is designed for a chair seat which is placed onto an underframe which is known per se and has a vertically inserted pneumatic spring for adjusting the height. In this case, the seat support, which is arranged right at the bottom of the seat, is placed onto the telescopically extendable piston rod of the pneumatic spring. The seat support supports a seat plate, and a pivotable back support is coupled on a main rotational axis which runs transversely above the seat plate, parallel to its front edge. An inclination spring is coupled at one end to the seat support on a fixed rotational axis and at the other end to the back support on a moving rotational axis. On its lower side the seat plate has guide cranks in which supporting arms of the seat support engage in a manner such that they can be displaced transverse to the main rotational axis. The seat plate is coupled to the back support, together with the inclination spring, on the moving rotational axis. Two spaced apart guide cranks are advantageously provided in the vicinity of the front edge of the seat plate, the guide cranks having an end limitation at the front as a stop. Bearing pegs which are arranged right at the front of the free ends of the supporting arms engage in the guide cranks.
Two arms of the back support, which arms extend laterally above the seat plate, and, in principle, two vertical branchesxe2x80x94these constitute angled extensions of transverse extension arms, running below the seat plate, of the seat support are connected to one another in an articulated manner in the main rotational axis. The branches each have a plug-in opening for receiving an armrest. The back support has a transverse strut which extends between the arms, parallel to the main rotational axis, and has two stays which run upward from the intersection of the transverse strut with the respective arm. Fastened to the transverse strut is an axial bar through which runs the moveable rotational axis with the hinged seat plate and the hinged inclination spring. A pneumatic spring with an attached helical spring is especially suitable as the inclination spring. A back cover is stretched between the arms, it being possible for a curved back tensioner to be attached to the arms, so that the arms are only of stump-shaped design.
A respective hinge plate is coupled to the axial rod on both sides of the hinged inclination spring, and the seat plate is fastened on the hinge plates at a variable distance from the rotational axis. A ball socket for holding a release ball is situated in the seat support, it being possible for said release ball to be moved via a cable pull and an operating lever against the valve rod of the pneumatic inclination spring, as a result of which the locking of the pneumatic inclination springxe2x80x94as an open connectionxe2x80x94is cancelled.
A lumbar reinforcing insertxe2x80x94in the form of a flexible platexe2x80x94which is height-displaceable and can be fixed at the height selected is arranged in the back cover. An upwardly protruding fixing tongue extends from the plate. The reinforcing insert is inserted into an upwardly open pocket which is incorporated in the back cover. On the fixing tongue which protrudes out of the back cover through a slot and on the back cover, fixing components, for example touch and close fasteners, for the releasable fastening are provided. In this manner, the selected height position of the lumbar reinforcing insert can be retained. On its lower edge the back cover is fixed on the rear side of the transverse strut. This advantageously takes place using fastening elements which protrude through the transverse strut and with which the axial rod is at the same time fastened to the transverse strut. The armrest has an approximately vertical stay with an arm support arranged at the top, a notched section having a systematic grid of notches being provided on the stay. The notches lie in a line one above another and are semicircular. The notched section is plugged into the plug-in opening in the raised branch of the seat support. A hole which the inserted notched section partially touches is made in this branch. Seated in the hole is an operating button which is supported by a spring and engages in a locking manner in the contour of a notch standing in position with respect to the operating button. The cross section of the stay is preferably elliptical, the notches lying on a main apex of the ellipse. The operating button is connected axially to a disk element of which a circular segment engages in the positioned notch.
The essential advantages of the adjusting mechanism reside in the efficiently and comfortably realized synchronization between the sequences of movement of the back support and seat plate. The chair is refined by means of height-adjustable armrests, the adjustment being easy to operate for the user and positions which are set being retained stably, even when subjected to a relatively great load. The lumbar reinforcing insert which can be inserted in a height-variable manner into the back cover provides an individually and rapidly positionable support for the lumbar region of the user.